With the progress of display technologies, more and more active matrix organic light emitting diode (AMOLED) display panels enter the market. In comparison with conventional thin film transistor liquid crystal displays (TFT LCDs), AMOLED display panels have advantages of low energy consumption, low production cost, self-luminescence, wide view angle, rapid response rate and the like. Currently, conventional LCD display screens have been displaced gradually by organic light emitting diode (OLED) display panels in the display areas such as mobile phone, personal digital assistant (PDA), digital camera and the like.